Buffering device for the operating mechanism of a switchgear, and method of lubrication thereof

ABSTRACT

A piston rod ( 15 ) and a first piston ( 13 ) are arranged in the interior of an external cylinder ( 11 ) and internal cylinder ( 12 ); a second piston for absorbing the change of volume of operating fluid ( 24 ) is also arranged therein. Also, a first return spring ( 18 ) for returning the piston rod ( 15 ) to the interruption position is provided and a second return spring ( 20 ) for returning the operating fluid  24  into the high-pressure chamber ( 25 ) by pressurizing the second piston ( 14 ) is provided. In addition, the air in the interior of the buffering device ( 10 ) is withdrawn by a vacuum pump ( 38 ), and operating fluid ( 24 ) is thus introduced in a degassed condition.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 13/501,047, filed Jun. 6, 2012, which is the U.S. NationalStage application of PCT/JP10/006006 filed Oct. 7, 2010, and whichclaims priority under 35 U.S.C. §119 to Japanese application number JP2009-234881 filed Oct. 9, 2009, the entire contents of which areincorporated by reference herein.

TECHNICAL FIELD

The present invention relates to an operating mechanism for a switchgearin which opening/closing operation of the switchgear is performed byoperating a moving body including an electrical contact, and, inparticular, it relates to a buffering device for braking the moving bodywhen operation is performed, and to a method of lubrication thereof.

BACKGROUND ART

In general, the operating mechanism for a high-voltage switchgear isoperated by opening/closing operation (interruption/closure operation)of the switchgear, by reciprocating drive of an electrical contact ofthe switchgear between the open and closed positions. In order for theswitchgear to exhibit good interruption performance, it is important forthe moving body including the electrical contact to be driven at highspeed by the operating mechanism.

In this process, it is desirable for the operating mechanism to maintainthe speed of the moving body until a little before it reaches the endposition of its interruption operation and then to reduce the speed ofthe moving body in a comparatively short distance. Consequently,usually, a buffering device constituting means for reducing the speed ofthe moving body is employed in the operating mechanism.

A first prior art example of such a buffering device is disclosed forexample in Laid-open Japanese Patent Gazette, Laid-open PatentApplication Number H9-303,467 (FIG. 1) (hereinafter referred to asPatent Reference 1) or, likewise, Laid-open Japanese Patent Gazette,Laid-open Patent Application Number 2008-291898 (FIG. 1) (hereinafterreferred to as Patent Reference 2). In this first prior art example, adouble-layer cylinder comprising outer and internal cylinders isprovided. Of these, the operating fluid is sealed within the externalcylinder. Also, buffer orifices are formed at both ends of the internalcylinder.

In addition, within the internal cylinder, a slide rod and piston areslidably arranged. The slide rod is coupled with the drive section of anoperating mechanism. Steps provided with a taper are arranged on bothsides of the piston. The steps at both ends of the piston are fittedinto the buffer orifices at both ends of the internal cylinder.

On the outside of the buffer orifices, a packing is arrangedconstituting a sealing section for preventing leakage of operating fluidthat is sealed within the external cylinder. It should be noted that theoperating fluid that flows out from the buffer orifices flows into theopposite side of the piston through an oil return passage that is formedfrom the gap between the external cylinder and the internal cylinder.

In a buffering device constructed as above, in the case of bothinterruption operation and closure operation, a slide rod (including apiston) that is coupled with the drive section of the operatingmechanism is operated, and, just before the termination of operation,the steps of the piston penetrate into the buffer orifices. From thisinstant, the pressure within the buffer orifices rises, and a largereaction i.e. braking force is generated tending to push the pistonback. By means of this braking force, it is possible to reduce the speedof the slide rod only just before termination of operation.

Also, a second prior art example of a buffering device for the operatingmechanism for a switchgear is disclosed in Japanese Laid-open PatentGazette, Laid-open Patent Application Number H 10-228847 (FIG. 1)(hereinafter referred to as Patent Reference 3). In this PatentReference 3, just as in the above first prior art example, adouble-layer cylinder is provided and a piston is freely slidablyarranged in the interior of the internal cylinder. Also, in the internalcylinder, there are formed a plurality of outflow holes for operatingfluid, along the circumferential direction. It should be noted that thepiston is directly coupled with the output shaft of the operatingmechanism.

In the above second prior art example, the number of outflow holes thatare in an open condition decreases with sliding movement of the piston.Consequently, the rate of flow of operating fluid out from the internalcylinder decreases, with the result that the pressure of the operatingfluid rises, generating braking force. Consequently, a large brakingforce is generated immediately prior to completion of operation, inreciprocal operation.

PRIOR ART REFERENCES Patent References

[Patent Reference 1] Laid-open Japanese Patent Application NumberH9-303467 (FIG. 1)

[Patent Reference 2] Laid-open Japanese Patent Application Number2008-291898 (FIG. 1)

[Patent Reference 3] Laid-open Japanese Patent Application NumberH10-228847 (FIG. 1)

OUTLINE OF THE INVENTION Problem that the Invention is Intended to Solve

However, the following problems have been noted regarding prior artexample 1 described above. Specifically, in order to obtain a largebraking force of the buffering device, it is necessary either to makethe pressure-receiving area that is formed by the difference between thecross-sectional area of the piston and the cross-sectional area of theslide rod large, or to generate high pressure.

In this connection, if the pressure-receiving area is made large, thepiston diameter becomes large, and the buffering device tends to becomebulky overall. It is therefore desired to raise braking performancewhile maintaining compactness by generating a large braking force by asmall cylinder and piston.

Also, prevention of loss of air tightness of the packing whichconstitutes the sealing section for preventing leakage of operatingfluid is vital when generating high pressure in order to obtain a largebraking force of the buffering device. In the buffering device accordingto the first prior art example, slide rods are arranged on both sides ofthe piston, so there are a large number of sliding sealing portions.

That is to say, in the packing in the first prior art example, pressureresistance tends to be lowered by sliding movement with respect to theslide rods. For example, in the case of packing such as an O ring,whereas when such packing is employed in a fixed portion it is capableof withstanding high pressure (about 1000 atm), when employed at asliding location, however, it can only withstand a pressure of abouthalf of that.

Furthermore, in the first prior art example, operating fluid, that hasreached a high pressure within the buffer orifices, flows out on thelow-pressure side of the piston through the oil return passages,reaching the packing. Consequently, the packing is exposed tohigh-pressure operating fluid, so the sealing member must be capable ofwithstanding high pressure.

Consequently, the packing of the first prior art example is employed ina sealing portion where it is subjected to sliding under high pressure,so it not only needs to be resistant to pressure but also resistant towear: such packing is expensive. Indeed, the provision of a large numberof expensive packing elements capable of preventing loss ofair-tightness of the packing gives rise to severe cost problems.

Furthermore, in the case of the buffering device of the first prior artexample, in which slide rods are arranged on both sides of the piston, aconstruction must be adopted in which the volume of the operating fluidin the cylinder does not change. Consequently, with the object ofadjusting for volume changes of the operating fluid, although not shown,typically a component construction is adopted in which entrainment ofair from the sealing section of the slide rods occurs: this results inair accumulating within the cylinder.

Also, since the buffering device is basically a device in which brakingforce is generated by conversion of pressure energy into heat energy,since the operating fluid becomes highly pressurized when the device isoperated, the temperature inevitably rises. Furthermore, sinceenvironmental temperature changes also take place, if the working fluidis hermetically sealed within a metal container, it is necessary tocreate a slight air layer, to take into account the difference inthermal expansion of the metal and the operating fluid (a factor ofabout 100 times or more).

If the air of this air layer becomes mixed with the operating fluid, theviscosity of the operating fluid is lowered, so the braking forcechanges. In particular, in the case where the switchgear is aninterrupter and high-speed reclosing interruption operation isperformed, since the interruption action takes place twice in a shorttime (0.3 sec), if air is mixed with the operating fluid in the firstinterruption operation, there is a risk that the braking force duringthe second interruption operation will be considerably different fromthat during the first interruption operation. There is therefore astrong demand to avoid mixing of the air with the operating fluid.

Also, in the case of the second prior art example, an air layer isprovided because the volume of the operating fluid changes with themovement of the piston. Consequently, there were the problems that theattitude in which the buffering device can be mounted is restricted andthat the braking force changes as a result of admixture of the air withthe operating fluid, as described in connection with the problems of thefirst prior art example in the above section.

Furthermore, in the second prior art example, the piston of theoperating mechanism is directly coupled with the output shaft.Consequently, when the switchgear performs opening/closing operation(interruption/closure operation), the piston is always the load, sobraking force acts over the entire stroke. As a result, the brakingforce of the buffering device also acts during the closure operation ofthe switchgear, and this is associated with a loss in drive energy ofthe operating mechanism. The result is that the efficiency ofutilization of the drive energy is lowered. It should be noted that lossof drive energy of the operating mechanism was also a problem whensealing portions were present that were subjected to sliding at highpressure, as in the case of the first prior art example described above,due to the increase in frictional force of the sliding sections (slidingresistance).

As described above, with the conventional buffering devices, generationof large braking force with a small cylinder and piston required thatsealing portions sliding under high pressure should be eliminated,admixture of air with the operating fluid should be discouraged, andthat the drive energy of the operating mechanism should be efficientlyutilized.

Incidentally, since, in the buffering device, the operating fluid had tobe made to penetrate into narrow gaps between components, pressurizationand lubrication of the operating fluid were necessary. Also, if airbecame mixed with the operating fluid during the lubrication, the taskof extracting this air was indispensable, and this meant that a longtime was required for the lubrication task.

This embodiment of the present invention was made in order to solve theabove problems, its object being to provide a buffering device for theoperating mechanism of a switchgear that performs opening/closing of anelectrical circuit, capable of maintaining in a stable fashion a largebraking force while achieving compactness and capable of utilizingefficiently the drive energy of the operating mechanism and of improvingreliability with regard to leakage of the operating fluid, with lowcost, without directly applying high pressure to the sliding sealingportions; and, in addition, of providing a method of lubrication of thebuffering device whereby the lubrication task of the buffering devicecan be performed in a short time.

Means for Solving the Problem

In order to achieve the above object, according to an embodiment of thepresent invention, there is provided: a buffering device employed in anoperating mechanism whereby opening/closing action of a switchgear isperformed by reciprocal drive of a moving body including an electricalcontact between open and closed positions, for reducing the speed ofsaid moving body in the vicinity of termination of the action of theswitchgear, characterized in that:

an external cylinder and internal cylinder are provided on the samecentral axis; a first piston is arranged within aforementioned internalcylinder, and a second piston is arranged within aforementioned externalcylinder, these being respectively freely slidably arranged on the samecentral axis; a piston rod is freely slidably arranged with respect toaforementioned first piston and aforementioned second piston; a packingis fixed in aforementioned second piston in a sliding portion ofaforementioned external cylinder and aforementioned piston rod; a firstreturn spring seat is fitted at the end of aforementioned piston rod, inorder to restrict the range of movement of aforementioned first piston;a first return spring is arranged between the end of aforementionedinternal cylinder and aforementioned first return spring seat; a secondreturn spring seat is fixed on the same central axis withinaforementioned external cylinder; a second return spring is arrangedbetween aforementioned second piston and aforementioned second returnspring seat; an oil return path is formed between aforementioned pistonrod and aforementioned first return spring seat and one end thereof isopened/closed by sliding action of aforementioned first piston; aplurality of through-holes are formed in the axial direction inaforementioned internal cylinder; a plug having a packing is fixed atthe end of aforementioned internal cylinder; a high-pressure chamber isformed by the space defined by aforementioned external cylinder,aforementioned internal cylinder, aforementioned plug, aforementionedsecond piston and aforementioned piston rod; aforementioned plug beinglinked with a drive portion of aforementioned operating mechanism;operating fluid is sealed in aforementioned high-pressure chamber; andthe construction is such that braking force is generated by compressionof aforementioned operating fluid of aforementioned high-pressurechamber by aforementioned piston rod being forced into aforementionedhigh-pressure chamber on drive of aforementioned operating mechanism.

Beneficial Effect of the Invention

With the buffering device of this embodiment of the present invention,the operating fluid can be utilized in a high-pressure condition at thepiston portion, so a large braking force can be generated with asmall-diameter piston and cylinder, so reduction in size and weight ofthe device can be promoted. Also, since the high pressure is notdirectly applied to the sliding sealing portion, expensive packing canbe eliminated, contributing to lower costs and improving reliabilitywith regard to leakage of operating fluid.

Furthermore, the construction is one in which change in volume of theoperating fluid can be absorbed by combination of the second piston withthe second return spring: in this way, there is no need for an air layeron the operating fluid, so stable braking force can be obtained byreliably preventing admixture of the air with the operating fluid.Furthermore, the braking force of the buffering device does not actduring the closure operation of the switchgear, so there is no loss ofdrive energy of the operating mechanism, so improving the efficiency ofutilization of the drive energy. Also, with the method of lubrication ofthe buffering device of this embodiment of the present invention, no airis mixed with the operating fluid, so the lubrication task can beperformed rapidly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing the closure condition of abuffering device for the operating mechanism of a switchgear accordingto a first embodiment of the present invention;

FIG. 2 is a cross-sectional view showing the interruption condition ofthe buffering device of FIG. 1;

FIG. 3 is a view of the buffering device of FIG. 2 in the direction ofthe arrows A-A;

FIG. 4 is a detail view to a larger scale showing a portion of thebuffering device of FIG. 2;

FIG. 5 is a cross-sectional view showing the closure condition of abuffering device for the operating mechanism of a switchgear accordingto a second embodiment of the present invention;

FIG. 6 is a cross-sectional view showing the closure condition of abuffering device for the operating mechanism of a switchgear accordingto a third embodiment of the present invention;

FIG. 7 is a cross-sectional view showing the interruption condition ofthe buffering device of FIG. 6;

FIG. 8 is a cross-sectional view showing a method of lubrication of abuffering device for the operating mechanism of a switchgear accordingto a fourth embodiment of the present invention;

FIG. 9 is a cross-sectional view showing a method of lubrication of abuffering device for the operating mechanism of the switchgear accordingto a fifth embodiment of the present invention.

EMBODIMENTS OF THE INVENTION

Embodiments of a buffering device for the operating mechanism of theswitchgear according to the present invention and a method oflubrication thereof are described below with reference to the drawings.

[1] First Embodiment Construction

First of all, a first embodiment of a buffering device for the operatingmechanism of the switchgear according to the present invention will bedescribed with reference to FIG. 1 to FIG. 4. FIG. 1 is across-sectional view showing the closure condition of a buffering device10 for the operating mechanism of a switchgear; FIG. 2 is across-sectional view showing the interruption condition of the bufferingdevice 10 shown in FIG. 1. FIG. 3 is a view of the buffering device ofFIG. 2 in the direction of the arrows A-A. FIG. 4 is a detail view to alarger scale showing a portion of the buffering device of FIG. 2.

The buffering device 10 serves to reduce the speed of the movablecontact 1 constituting the moving body in the operating mechanism of theswitchgear. Operating fluid 24 is sealed in the interior of thebuffering device 10: braking force is generated by compression of theoperating fluid 24 immediately before arrival at the terminal positionof movement of the movable contact 1.

As shown in FIG. 1 and FIG. 2, a support structural body 6 is providedin the operating mechanism of the switchgear. An interruption spring 2is accommodated in the interior of the support structural body 6 and arestraining plate 7 is fixed at the end thereof. An interruption springseat 4 is mounted at the movable end 3 of the interruption spring 2,facing the aforementioned restraining plate 7. Also, a spring rod 5 iscoupled with the movable contact 1 through a linkage section 8: thebuffering device 10 is provided so as to be clamped by this spring rod 5and interruption spring seat 4.

The buffering device 10 comprises: double-layer cylinders 11, 12 anddouble-layer pistons 13, 14 having the same central axis; a unitarypiston rod 15, two packings 16, 22, two return springs 18, 20, thespring seats 17, 19 of these return springs, and a plug 23.

The construction of the buffering device 10 referred to above will nowbe described in detail. One end of the external cylinder 11 is fixed tothe interruption spring seat 4 and this external cylinder 11 extendstowards the spring rod 5. The internal cylinder 12 is telescopicallyfitted in the interior of this external cylinder 11.

The first piston 13 is arranged on the inside of the internal cylinder12 and the second piston 14 is freely slidably arranged on the inside ofthe external cylinder 11, respectively. In the closure condition shownin FIG. 1, the second piston 14 is stationary in a condition makingcontact with the end of the internal cylinder 12, and the first piston13 is stationary in a condition contacting the second piston 14.

Also, the first piston 13 and second piston 14 are adjacent to eachother in the closure condition as shown in FIG. 1, but, in theinterruption condition, are slid in the direction such as to separatethese, as shown in FIG. 2. Specifically, when the movable contact 1moves from the closure condition to the interruption condition (from thecondition of FIG. 1 to the condition of FIG. 2), the first piston 13moves to the right-hand side in the Figure and the second piston 14moves to the left-hand side in the Figure.

The piston rod 15 is arranged so as to be freely slidable with respectto the first piston 13 and the second piston 14. The packings 16 areprovided in the second piston 14 at the sliding portion of the externalcylinder 11 and the piston rod 15. Also, a piston head 15 b is providedat the end (left-hand side end in FIG. 1 and FIG. 2), nearest to therestraining plate 7, on the piston rod 15. This piston head 15 bcomprises a circular convex surface section 15 c having a gently convexsurface facing the restraining plate 7, and a flat surface 15 d facingthe side of the interruption spring seat 4.

The circular convex surface section 15 c of the piston head 15 b iscapable of being moved into contact with or away from the restrainingplate 7 and its diameter is set to be less than the diameter of thepiston rod 15. Also, in the piston head 15 b, the flat surface 15 d thatis positioned on the opposite side to the circular convex surfacesection 15 c is engaged with the end of the external cylinder 11 that isfixed to the interruption spring seat 4 in such a way that it can befreely separated therefrom.

In the closed condition shown in FIG. 1, the circular convex surfacesection 15 c of the piston head 15 b is separated from the restrainingplate 7 and the flat surface 15 d on the opposite side is separated fromthe end of the external cylinder 11. From this closed condition, in theinterruption condition shown in FIG. 2, the circular convex surfacesection 15 c of the piston head 15 b contacts the restraining plate 7and, furthermore, the flat surface 15 d of the piston head 15 b and theend of the external cylinder 11 are in contact and stationary.

In addition, a first return spring seat 17 that restricts the range ofmovement of the first piston 13 is fitted at the end (right-hand sideend in FIG. 1 and FIG. 2) on the opposite side of the piston head 15 b,on the piston rod 15. Also, between the piston rod 15 and the firstreturn spring seat 17, this one end is formed with an oil return path 15a that is opened and closed by sliding action of the first piston 13.Furthermore, a first return spring 18 is arranged between the firstreturn spring seat 17 and the end of the internal cylinder 12. The firstreturn spring 18 has the function of returning the piston rod 15 to theinterruption position.

A second return spring seat 19 with the same central axis is fitted onthe inside of the external cylinder 11. A second return spring 20 isarranged between the second return spring seat 19 and the second piston14. Due to the combination of this second return spring 20 and thesecond piston 14 referred to above, change in volume of the operatingfluid 24 in the high-pressure chamber 25 can be absorbed.

A plurality of through-holes 21 are formed in the internal cylinder 12.In addition, a plug 23 is arranged at the end of the internal cylinder12, a packing 22 being fixed to this plug 23. Also, the plug 23 isfitted onto a threaded section 5 a that is formed at the end of thespring rod 5. The space defined by the external cylinder 11, theinternal cylinder 12, the plug 23, the second piston 14 and piston rod15 constitutes a high-pressure chamber 25: the operating fluid 24 issealed therein.

Also, between the second piston 14 and a second return spring seat 19, acollar 26 having the same central axis as the piston rod 15 is freelyslidably arranged with respect to the piston rod 15. This collar 26 is amember for restricting the height of compression of the second returnspring 20.

When the operating fluid 24 in the high-pressure chamber 25 iscompressed by the action of the first piston 13, the space into whichthe operating fluid 24 is injected from the through-hole 21 constitutesa low-pressure chamber 27. Also, as shown in FIG. 2, in the interruptioncondition, the first piston 13 and the second piston 14 are separatedand a liquid chamber 28 is formed constituting the space defined bythese pistons 13, 14 and the piston rod 15.

The operating fluid 24 that has flowed out from the through-holes 21into the low-pressure chamber 27 flows in from the low-pressure chamber27 to the liquid chamber 28. Cutaway sections 12 a and projections 12 bto obstruct the flow of the operating fluid 24 are then arranged at theend of the internal cylinder 12; the projections 12 b are arranged insubstantially the same plane as the through-holes 21 (see FIG. 3).

Incidentally, while, as shown in FIG. 4, the packings 16 are provided atthe sliding portion of the external cylinder 11 and the piston rod 15 inthe second piston 14, in more detail, these packings are fixed at tworespective locations at the outer circumference and inner circumferenceof the second piston 14. An outer circumferential groove 14 a is formedbetween the two packings 16 on the outer circumferential side and aninner circumferential groove 14 b is formed between the two packings 16on the inner circumferential side. Also, a plurality of through-holes 14c that link these two are arranged between the outer circumferentialgroove 14 a and the inner circumferential groove 14 b. A space foraccumulation of operating fluid 24 is formed by means of the outercircumferential groove 14 a, inner circumferential groove 14 b andthrough-holes 14 c.

(Interruption Action)

The interruption action, from the closed condition shown in FIG. 1 tothe interrupted condition shown in FIG. 2 in the first embodimentconstructed in this way will now be described. When an interruptioninstruction is delivered to the operating mechanism of the switchgear,not shown, from a control device, not shown, the interruption spring 2starts the interruption action. When the interruption spring 2 hasextended by a certain fixed distance, the circular convex surfacesection 15 c of the piston head 15 b abuts the restraining plate 7.

From this instant, the piston head 15 b and the piston rod 15 startmovement towards the side of the spring rod 5. The first piston 13blocks one end of the oil return path 15 a of the piston rod 15 andstarts compression of the operating fluid 24 in the high-pressurechamber 25. The first piston 13 blocks a plurality of through-holes 21but forces the operating fluid 24 in the high-pressure chamber 25 outtowards the low-pressure chamber 27 through the open through-holes 21.In this process, the pressure generated in the high-pressure chamber 25provides braking force, which is transmitted between the piston rod 15and the spring rod 5, providing a force which halts the action of theinterruption spring 2.

The flow of operating fluid 24 flowing into the low-pressure chamber 27is temporarily held up by the projections 12 b that are arranged insubstantially the same plane as the through-holes 21, but the operatingfluid flows out into the liquid chamber 28 from the portions where theprojections 12 b are absent i.e. the cutaway portions 12 a. The firstreturn spring 18 is compressed with movement of the piston rod 15 andthe first return spring seat 17.

The volume of the operating fluid 24 that has flowed into the liquidchamber 28 increases with movement of the second piston 14 towards thepiston head 15 b. The second piston 14 is subjected to pressure by thespring force of the second return spring 20 as it moves towards thesecond return spring seat 19, until it is arrested, having undergone afixed displacement, by the collar 26. FIG. 2 shows the condition inwhich this interruption action has been completed.

(Closure Action)

Next, the closure action from the interruption condition shown in FIG. 2to the closure condition shown in FIG. 1 will be described. When aninterruption instruction is delivered to the operating mechanism of theswitchgear, not shown, from a control device, not shown, theinterruption spring 2 starts the interruption action, by means of aclosure spring, not shown. In the case of the closure action, theinterruption spring 2 starts movement in the opposite direction (closuredirection) to the interruption direction, and movement of the spring rod5, which is linked with the interruption spring 2, the external cylinder11 and the internal cylinder 12 in the closure direction is commenced.

At this point, since the piston rod 15 is slidable with respect to theexternal cylinder 11 and internal cylinder 12, it tries to stay in theinterruption position. Since the second piston 14 starts movementtogether with the external cylinder 11, the operating fluid 24 in theliquid chamber 28 is compressed, the first piston 13 moves in thedirection of the first return spring seat 17, the oil return path 15 ais opened, and a flow path to the liquid chamber 28 and high-pressurechamber 25 is formed.

With further progress of the closure action, the piston rod 15 is forcedout towards the restraining plate 7 by the spring force of the firstreturn spring 18 and the operating fluid 24 that is pressurized by thesecond piston 14 and the second return spring 20 flows into thehigh-pressure chamber 25 through the oil return path 15 a, low-pressurechamber 27 and the plurality of through-holes 21. When the closureaction terminates, the second piston 14 is arrested in a positioncontacting the end of the internal cylinder 12, and the first piston 13is arrested in a position contacting the second piston 14. Thecompletion condition of the closure condition as described above isshown in FIG. 1.

(Beneficial Effects)

The beneficial effects of the first embodiment described above are asfollows. Specifically, in the first embodiment, the piston rod 15 thatprojects to the atmosphere side is in a single location. Consequently,the cross-sectional area of the first piston 13 can be made large.

Also, there is no need to provide packing for sealing while sliding inthe high-pressure chamber 25 that is compressed by the first piston 13.Consequently, the operating fluid 24 that is sealed into thehigh-pressure chamber 25 can be kept in a high-pressure condition. Inthis way, a large braking force can be generated with a small-diameterfirst piston 13 and internal cylinder 12, making it possible to reducethe size and weight of the device.

Furthermore, during braking by the buffering device 10, the operatingfluid 24 is reduced in pressure by passing through the through-holes 21from the internal cylinder 12 and flows out through the cutaway sections12 a constituted by the gaps of the projections 12 b from thelow-pressure chamber 27 to the liquid chamber 28, and the pressure ofthe operating fluid 24 is thereby further lowered.

As a result, there is no possibility of the packings 16 that areprovided in the sliding portion of the external cylinder 11 and thepiston rod 15 being subjected to the action of operating fluid 24 inhigh-pressure condition. In this way, inconveniences such as leakage ofoil can be reduced, and use of expensive sealing members madeunnecessary, thereby achieving cost reduction.

Also, in the first embodiment, the second piston 14 and the secondreturn spring 20 perform the function of adjusting for the change ofvolume of the operating fluid 24 within the buffering device 10.Consequently, it is unnecessary to provide an air layer on the operatingfluid 24 within the buffering device 10. In this way, admixture of airwith the operating fluid 24 is minimized and considerable stabilizationof the braking force of the buffering device 10 can be achieved.

Furthermore, thermal expansion of the operating fluid 24 due totemperature change can be absorbed by the second piston 14 and thesecond return spring 20. Consequently, leakage of oil from the interiorof the buffering device 10 and/or penetration of the air from theoutside can be prevented, considerably increasing the reliability inregard to leakage of the operating fluid 24.

Also, as shown in FIG. 4, an external circumferential groove 14 a andinternal circumferential groove 14 b are formed and through-holes 14 care arranged between the two packings 16 in the second piston 14, whilea storage space for the operating fluid 24 is formed from the spacebetween these. Consequently, even if traces of operating fluid 24 arescraped out by the piston rod 15, this operating fluid 24 can beaccumulated in the aforementioned accumulation space between the twopackings 16. It is thereby possible to prevent the operating fluid 24from being put into a high-pressure condition and leaking to theoutside, and entrainment of air from outside the buffering device 10 canbe minimized.

Also, when the switchgear is a circuit breaker and high-speed re-closureand interruption action is performed in which a second interruptionaction is implemented in a short time (within 0.3 sec), the first piston13 and the piston rod 15 must be returned to their prescribed positions.In the first embodiment, the first piston 13 and the piston rod 15 aremoved by the action of the first return spring 18. Also, the pressurizedoperating fluid 24 in the liquid chamber 28 can be returned from the oilreturn path 15 a of the piston rod 15 and the through-holes 21 into thehigh-pressure chamber 25 by the second return spring 20 and the secondpiston 14. In this way, the first piston 13 and the piston rod 15 can berapidly returned to their original positions.

Also, the second piston 14 is forced onto the second return spring 19 bythe pressure of the operating fluid 24 flowing into the liquid chamber28 from the low-pressure chamber 27, with the result that the secondreturn spring 20 is compressed. If the pressure at this point is largerthan the force of the second return spring 20, there is a possibilitythat the second return spring 20 may get stuck. If the second returnspring 20 gets stuck, damage occurs between the bare wires, with therisk that the durability of the spring itself may be lowered.Accordingly, in the first embodiment, generation of this inconvenienceis prevented by providing a collar 26 that restricts the height of thecompression of the second return spring 20.

Furthermore, as shown also in FIG. 7, by making the diameter of thecircular convex surface section 15 c (i.e. the diameter of the circularsection that makes planar contact with the spring rod 5 on the side ofthe opposite face) of the piston head 15 b less than the diameter of thepiston rod 15, it is possible to keep the bending force acting on thepiston rod 15 small while employing a large contact area, when thepiston head 15 b collides with the restraining plate 7. In this way,mechanical strength and reliability of the piston rod 15 can beimproved.

Incidentally the reason for referring to FIG. 7, which is describedlater, is that it might not be altogether easy to identify what is meantby the diameter of the circular convex surface section 15 c in FIG. 1.

[2] Second Embodiment Construction

Next, a second embodiment of a buffering device for the operatingmechanism of a switchgear according to the present invention will bedescribed with reference to FIG. 5. FIG. 5 is a cross-sectional viewshowing the closed condition of the second embodiment of a bufferingdevice for the operating mechanism of a switchgear. It should be notedthat parts that are identical with or similar to corresponding parts inthe first embodiment are given the same reference numerals, to avoidduplication of description.

In the second embodiment, the mounting position of the buffering device10 shown in FIG. 1 and the construction of the plug 23 and second returnspring seat 19 are altered. Specifically, a construction is adopted inwhich the external cylinder 11 is fixed to the restraining plates 7, thespring rod 5 is fixed to the interruption spring seat 4, and the end ofthe spring rod 5 and the end of the piston rod 15 are engaged in such away that they can be freely brought into contact or separated.

Also one end of the plug 23 projects into the interior of the internalcylinder 12 and is engaged with a step 12 a of the internal cylinder 12in such a way that it can be freely separated therefrom, so that an airchamber 29 is formed from the internal cylinder 12 and plug 23.Furthermore, a plug hole 23 a is formed in the plug 23 so as to link thehigh-pressure chamber 25 and the air chamber 29. A throttle valve 30having an extremely small flow path is arranged on the side of thehigh-pressure chamber 25 in the plug hole 23 a, so that the air in theoperating fluid 24 is shut into the high-pressure chamber 29. Also,projections 19 a are arranged at the outer circumference of the secondreturn valve seat 19 and the collar 26 that is employed in the firstembodiment is dispensed with.

(Interruption Action)

In the second embodiment constructed as above, during interruptionaction, the same action as in the case of the first embodiment isperformed; however, a difference is that the circular convex surfacesection 15 c of the piston head 15 b abuts the end of the spring rod 5rather than the restraining plate 7. A further difference is that thesecond piston 14 abuts the projections 19 a of the second return springseat 19 rather than the collar 26.

(Closure Action)

It should be noted that, in the second embodiment, in closure action,the same action as in the case of the first embodiment is performed: theclosure action in the second embodiment can thus be easily deduced fromthe description of the interruption action given above, so a detaileddescription thereof is dispensed with.

(Beneficial Effect)

In addition to the same beneficial effects as in the case of the firstembodiment described above, in the second embodiment constructed asdescribed above, owing to the formation of the air chamber 29 defined bythe internal cylinder 12 and plug 23, the air in the high-pressurechamber 25 can pass through the plug hole 23 a into the air chamber 29,where it is trapped.

In this way, admixture of air with the operating fluid 24 on the side ofthe high-pressure chamber 25 can be reliably eliminated, making itpossible to promote stabilization of the braking performance. At thesame time, restrictions on the attitude of mounting of the bufferingdevice 10 can be eliminated, so the degrees of freedom regardinginstallation of the buffering device 10 can be increased.

Also, the buffering device 10 in the second embodiment is fixed at theside of the restraining plate 7 of the support structure 6 of theoperating mechanism of the switchgear rather than installed on theinterruption spring 2. Consequently, there is no possibility of thebuffering device 10 being driven with movement of the interruptionspring 2. As a result, no loss in drive energy of the operatingmechanism can occur in this way, so the efficiency of utilization of thedrive energy is further increased. It should be noted that, in thesecond embodiment, the beneficial effect produced by the collar 26 canbe achieved by the provision of projections 19 a on the second returnspring seat 19, so the number of members can be cut by eliminating thecollar 26.

[3] Third Embodiment Construction

Next, a third embodiment of the buffering device for the operatingmechanism of a switchgear according to the present invention will bedescribed with reference to FIG. 6 and FIG. 7. FIG. 6 is across-sectional view showing the closure condition of the thirdembodiment and FIG. 7 is a view showing the interruption condition ofthe device of FIG. 6. It should be noted that parts that are identicalwith or similar to corresponding parts in the first embodiment and asecond embodiment are given the same reference numerals, to avoidduplication of description.

The third embodiment is an improvement on the second embodiment and ischaracterized in that the construction is modified by dispensing withthe first return spring 18 of the buffering device 10 shown in FIG. 5.Specifically, a stud 32 extending on the opposite side to that of themovable contact 1 is provided on the restraining plate 7 and a cylinderfixing plate 31 is mounted on the stud 32.

An external cylinder 11 is fixed between this cylinder fixing plate 31and the restraining plate 7. An internal cylinder 12 a having the samecentral axis is freely slidably arranged on the inside of the externalcylinder 11 and a first piston 13 having the same central axis is freelyslidably arranged on the inside of the internal cylinder 12.

Also, a first piston 13 is fixed to the end of the piston rod 15, apiston head 15 b is fixed at the other end of the piston rod 15, and asecond piston 14 having the same central axis is freely slidablyarranged within the external cylinder 11. In addition, a packing 16 isfixed to the second piston 14 in the sliding portion of the externalcylinder 11 and the piston rod 15.

Also, a return spring 33 is arranged between the end of the secondpiston 14 and the piston head 15 b. Furthermore, a plurality ofthrough-holes 21 are arranged in the internal cylinder 12 and operatingfluid 24 is sealed in a high-pressure chamber 25 constituting the spacedefined by the external cylinder 11, internal cylinder 12, second piston14 and piston rod 15.

When the end of the spring rod 5 that is fixed to the interruptionspring seat 4 comes into contact with the circular convex surfacesection 15 c of the piston head 15 b and presses thereon, the operatingfluid 24 in the high-pressure space 25 that is defined by the firstpiston 13 and the internal cylinder 12 is compressed, raising itspressure. Braking force of the buffering device 10 is thereby generated.Also, a ring 34 having the function of restraining the height ofcompression of the return spring 33 referred to above and the functionof positional location is arranged between the external cylinder 11 andthe restraining plate 7.

(Interruption Action)

In the third embodiment constructed as above, in interruption action,the same action is performed as in the case of the first embodiment andsecond embodiment, but the planar surface section 15 d (opposite face tothe circular convex surface section 15 c) of the piston head 15 b abuts(see FIG. 7) the restraining plate 7. Also this embodiment differs inthat the second piston 14 abuts the ring 34.

(Closure Action)

Also, the same closure action is performed in the third embodiment as inthe case of the second embodiment: however, the following points aredifferent. Specifically, with extension of the return spring 33, thespring force of the return spring 33 is applied to the second piston 14,with the result that the operating fluid 24 in the liquid chamber 28 israpidly returned to the high-pressure chamber 25 through thethrough-holes 21, so that return to the closed condition of the pistonrod 15 can be rapidly effected. The details of the action can easily beinferred from the first embodiment and second embodiment, so a detaileddescription thereof may be dispensed with.

(Beneficial Effect)

In addition to the beneficial effects possessed by the first and secondembodiments described above, the third embodiment constructed as abovehas the following independent beneficial effect. Specifically, byarranging the return spring 33 between the piston rod 15 and the secondpiston 14, the two actions of return of the piston rod 15 and return ofthe operating fluid 24 of the liquid chamber 28 to the high-pressurechamber 25 can be achieved by a single member.

In this way, the requirement to form an oil return path 15 a in thepiston rod 15 is eliminated and the layout of the members can besimplified. Furthermore, the overall length of the buffering device 10can be reduced and the number of components also reduced: thiscontributes to increased compactness and lower costs.

[4] Fourth Embodiment Construction

In addition, a method of lubricating a buffering device for theoperating mechanism of a switchgear according to a fourth embodiment ofthe present invention is described with reference to FIG. 8. FIG. 8 is across-sectional view showing the construction of a fourth embodiment ofthe present invention.

As shown in FIG. 8, a lubricating plug 35 is inserted in place of theplug 23 and this lubricating plug 35 is connected with a conduit 36. Apacking 37 is fixed in the vicinity of the tip of the lubricating plug35. At some point, the conduit 36 is branched in two directions, one ofthese branches being connected with a vacuum pump 38 while the other isconnected with the container 39 that accumulates operating fluid 24. Inthe conduit 36, a first valve 40 is arranged on the side of the vacuumpump 38 and a second valve 41 is arranged on the side of the container39.

(Method of Lubrication)

In a buffering device 10 constructed as above, when the operating fluid24 is introduced into the interior, the first valve 40 is opened and thesecond valve 41 is put into a closed condition; the interior of thebuffering device 10 is then evacuated to a vacuum condition using thevacuum pump 38; next, by closing the first valve 40 and opening thesecond valve, the operating fluid 24 in the container 29 is introducedinto the interior of the buffering device 10. Thus, as the operatingfluid that is here employed, operating fluid is used that has beendegassed beforehand in the vacuum container to remove air etc in theoil.

(Beneficial Effect)

With the fourth embodiment, operating fluid 24 that has been degassed byputting the interior of the buffering device 10 into a vacuum conditionusing the vacuum pump 38 is employed for lubrication, so gas such as airis substantially absent in the interior of the buffering device 10.Fluctuation of the braking force resulting from admixture of air withthe operating fluid 24 can therefore be prevented. Furthermore, theoperating fluid 24 can be made to enter all the narrow spaces betweenthe components, without needing to introduce the operating fluid 24 intothe interior of the buffering device 10 under pressure. In this way, thetask of removing internal bubbles is eliminated, making it possible togreatly reduce the time for the lubrication task.

[5] Fifth Embodiment Construction

A second method of lubrication of a buffering device for the operatingmechanism of the switchgear according to a fifth embodiment of thepresent invention is described with reference to FIG. 9. FIG. 9 is across-sectional view showing the construction of a fifth embodiment ofthe present invention. Parts that are identical with or similar to thoseof the fourth embodiment are given the same reference symbols, to avoidrepetition of description.

A construction is adopted in which partial cutaway sections 35 a areformed at the tip of the lubricating plug 35 of FIG. 9, and the plug 23is pushed into the interior of the internal cylinder 12. Consequently,when cancelling the amount of the change in volume produced by theinsertion of the target 35 into the interior of the internal cylinder12, the space into which the operating fluid 24 in the buffering device10 enters is expanded by fitting of a plate 42 between the piston head15 b and the end of the external cylinder 11. Other details of theconstruction are substantially the same as in the case of the fourthembodiment.

(Method of Lubrication)

The procedure for introduction of the operating fluid 24 into theinterior of the buffering device 10 is substantially the same as in thecase of the fourth embodiment; however, the plate 42 may be removedafter removing the lubricating plug 35.

(Beneficial Effect)

The same beneficial effects as in the case of the fourth embodimentdescribed above may also be obtained with the construction as above.

[6] Other Embodiments

The embodiments described above are purely by way of example and thepresent invention is not restricted to these embodiments. For example,although, in the above embodiments, compression coil springs wereemployed for the first return spring 18 and second return spring 20 andreturn spring 33, other resilient elements such as for example a dishspring or plate spring could be employed.

POSSIBILITIES OF INDUSTRIAL APPLICATION

The present invention can be applied to switchgears for powerinterruption.

What is claimed is:
 1. A buffering device employed in an operatingmechanism whereby opening/closing action of a switchgear is performed byreciprocal drive of a moving body including an electrical contactbetween open and closed positions, for reducing the speed of said movingbody in a vicinity of termination of an action of a switchgear, saidbuffering device comprising: (1) an external cylinder and internalcylinder that are provided on a same central axis; (2) a first pistonarranged within said internal cylinder, freely slidably arranged on saidsame central axis; (3) a second piston respectively arranged within saidexternal cylinder freely slidably arranged on said same central axis;(4) a piston rod freely slidably arranged with respect to said firstpiston and said second piston; (5) a packing fixed in said second pistonin a sliding portion of said external cylinder and said piston rod; (6)a first return spring seat that is fitted at an end of said piston rod,in order to restrict a range of movement of said first piston; (7) afirst return spring that is arranged between an end of said internalcylinder and said first return spring seat; (8) a second return springseat that is fixed on said same central axis within said externalcylinder; (9) a second return spring that is arranged between saidsecond piston and said second return spring seat; (10) an oil returnpath that is formed between said piston rod and said first return springseat and one end of which is opened/closed by sliding action of saidfirst piston; (11) a plurality of through-holes formed in an axialdirection in said internal cylinder; (12) a plug having a packing, thatis fixed at an end of said internal cylinder; (13) a high-pressurechamber formed by a space defined by said external cylinder, saidinternal cylinder, said plug, said second piston and said piston rod,said plug being linked with a drive portion of said operating mechanism;(14) an operating fluid that is sealed in said high-pressure chamber,constructed in such a way that braking force is generated by compressionof said operating fluid by said piston rod being forced into saidhigh-pressure chamber on drive of said operating mechanism, wherein arestraining plate is fixed in a support structural body of saidoperating mechanism of said switchgear, and an interruption spring isaccommodated therein; said external cylinder is fixed to saidrestraining plate; said spring rod is fixed to said interruption springseat; an and of said spring rod and an end of said piston rod areengaged in such a way that said end of said spring rod and said end ofsaid piston rod can be freely moved into contact or separated; a step isprovided on said internal cylinder; one end of said plug projects intoan interior of said internal cylinder and is engaged with said stepformed on said internal cylinder in such a way that said plug ca befreely moved into contact or separated; an air chamber is formed by aspace defined by said internal cylinder and said plug; a plug hole forlinking said high-pressure chamber and said air chamber is formed insaid plug; a throttle valve having a flow path of exceedingly smalldiameter is arranged on a high-pressure chamber side of said plug hole;and constructed in such a way that air in said operating fluid is shutinto said air chamber.
 2. The buffering device of said operatingmechanism of a switchgear according to claim 1, further comprising apiston head that receives compressing force from outside is provided onsaid piston rod, wherein a diameter of said piston head is set to beless than a diameter of said piston rod.
 3. The buffering device of saidoperating mechanism of a switchgear according to claim 1, wherein aprojection such as to temporarily hold up a flow of said operating fluidinjected from said through-holes is arranged in substantially a sameplane as said through-holes, at an end of said internal cylinder.
 4. Thebuffering device of the operating mechanism of a switchgear according toclaim 1, wherein packings are respectively fixed at two locations on anouter circumference and inner circumference of said second piston; anouter circumferential groove is formed between said two packings on anouter circumferential side; an inner circumferential groove is formedbetween said two packings on an inner circumferential side; and saidouter circumferential groove and said inner circumferential groovecommunicate by means of through-holes, and a space for storage ofoperating fluid from said outer circumferential groove, said innercircumferential groove and said through-holes is formed.